Ultra short wave device



Feb 28, 1950 w. c. HAHN ULTRA SHORT WAVE DEVICE Filed June 1, 1938 3 Sheets-Sheet l Iriventor: William C.Ha'hr1,

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Feb.. 2s, 195o W. C. HAHN1 ULTRA SHORT WAVE DEVICE :s .sheets-sheet 2 Filed June l, 1938 Feb. 28, 1950 w. c. HAHN ULTRA SHORT WAVE DEVICE 3 Sheets-Sheet 3 .Filed June l, 1938 Inventor: William C. Hal'm,

by l-Ils ttorney.

`wave oscillators.

Patented Feb. 28, 1950 UNITED STATES PATENT OFFICE ULTRA snoRT WAVE DEVICE William C. Hahn, Scotia, N. Y., Iass'i'giio r to Gen-i eral Electric Compa York a corporation 'of New v Application June 1, 19378S'erial No. 211,123

(C1. S-39x 32 claims. l

flvly invention relates to discharge devices'and is especially applicable in connectionwith ultra short Wave oscillators, such as oscillators adapted .to operate at from live meters to five centimeters or less. The invention represents a further application of the principles set forth in my prior applcation Serial No. 153,602, filed July 14, 1937, .now U. S. Patent 2,220,839, granted November 5, 1940.

In the aforementioned application, it is pointed out that an lelectron stream may be modulated either as to electron velocity or as to #charge density. The first type of modulation involves -the production of systematic irregularities in electron velocity from point to point along the stream.

.The second involves the production of variations in charge density, such variations being manifested as systematic irregularities in the electron grouping.

In the conventional design of electronic discharge devices, no distinction is made between Y ly producing appreciable charge density variations in the vicinity of the control structure. The velocity modulation is subsequently and independently converted into charge density moduneed not be elaborated here, this expedient avoids lthe objectionable lowering of the input impedance which is observed in connection with prior art devices when they are operated at ultra high frelquencies.

-In application Serial No. 201,953, iiled April 14,

.1938, by G. F. Metcalf, now U. S. Patent 2,220,840,

vgranted November 5, 1940, there is disclosed and claimed broadly one means by which the velocity kmodulation principle may be applied to short It is an object of my present `invention to provide alternative and improved arrangements for fulfilling the same function.

The features of novelty which I desire to protect herein are pointed out with particularity in the appended claims. -The invention itself, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection `with ,the drawings in which Fig. 1 is a view lnlongilation of a higher order of magnitude so as tov produce amplification effects'. For reasons which l tudinal section of a discharge device suitably embodying the invention; Figs. 2 and 3 are imaginativeA representations useful in explaining the invention. Fig. 4 comprises a modification of the construction of Fig. 1; Fig. 5 is a longitudinal sectional view of an alternative embodiment of the invention; Fig'. 6 is a sectional View taken ,on` linesof Fig. 5; Fig. 7 shows a partial section of a furtherembodiment of the invention and Figs. 8 and l9 are two sectional views of a still further embodiment.

In Fig. 1, the elements at the left of the ligure constitute an electron gun for producing an electron beam. In the remaining figures, these elements have been omitted to conserve space, but their presence as a part of the illustrated combi# nation is to be understood.

Referring particularly to Fig. 1, there is shown tubular glass envelope which consists of an elongated shaft portion I and an enlarged anodecontaining kportion Il. vAt one extremity of the shaft portion, there is provided means for producing an electron beam, such means comprising any known type of felectron gun. The particular combination `illustrated includes a cathode i3, shown in dotted outline, a focusing cylinder i4' surrounding the cathode and electrically connect-v ed thereto and anaccelerating electrode I5 positioned adjacent to the focusing cylinder and maintained at a high potential with respect to the cathode.

At the opposite Aend of the envelope, there is provided an anode I1 which is adapted to receive electrons projected toward it from the cathode I3y and which may consist of graphite or an equivalent refractory material. Adjacent to the discharge-receiving face of the anode, there y is' provided a cylinder I8 which is adapted to serve as'a suppressor grid for intercepting secondary lelectrons emitted from the anode during operation. This'cylinderisordinarily maintained at a Anegative potential with respect to the anode.m

In'the intermediate portion of the envelope, there are provided a series of electrode elements 20 which serve to fix the potential of the interior surface of the envelope wall. These may suitably comprise bands of conducting material, for exam--` ple, resistance paint rapplied circumferentially to the interior wall surface. They are provided with lead-in yconnections A2l and spring contacts v222 which make it possible to apply a denite po, tential to the electrodes 20. With circuit connections such as those shown, the electrodes 20 are at ground potential, while-the cathode is maintained severalthousand volts negative by means of a battery 23. The accelerating electrode I5 is biased to a potential intermediate that of cathode and ground, and the anode I'I is held several thousand volts above the cathode by the use of a battery 2A. These potentials are, of course, exemplary and may be varied Within Wide limits.

In order to maintain the electron beam'rin focus during its passage through the envelope, there are provided a series of magnetic coils 25 mounted co-axially with the envelope. These may be excited with direct current and function in a known manner to prevent dispersion of the beam.,

In some cases, they may advantageously be replaced by electrostatic beam-focusing means.

The electrode combination which has been so far described comprises means for producing a unidirectional electron beam'of constant averagey intensity and velocity. My present invention provides means by which such a beam may be caused to produce ultra-high-frequency oscillations.

In order to effect such oscillations', there is provided a modulating space of the general char acter described in my aforesaid application Serial No. 153,602. This may comprise, for example, a tubular chamber 3i) having Wall portions 3l and 3I" which are transverse to the axis of the beam and which approach relatively closely tothe envelope wall. These Wallportions serve to fix the boundary potentials of the modulating space. They also assist in shielding the modulating space from the beam source (i. e; the cathoder I3) so that potential variations Which occur Within the space have no effect on the cathode emission. This shielding function is` improved' by the use of a tubular extension 32 projecting in the direction ofthe cathode.

Inmy aforementioned prior application, I ,have shown that if the potential of 'an intermediate region of a modulating space such as that described is alternately raised and' lowered with respect to the` boundary potentials,,velocityinodulation of the beam maybe produced. While numerous structures for accomplishingthis result are described 'in the said application, only one isV illustrated here. This comprises atubular control` electrode 35 having its extremities relatively close to the wall portions SI.' andV 3|". As,- suming that the potential ofjthis electrode isbeing alternately raised and'loWered by application of a control potential thereto, maximum velocity mod,- ulation of the beam will occur when the length ofthe electrodeisso correlated' to; the velocity of, the beam that the electron transit time therethrough corresponds approximatelyto one-half cycle (or an odd number of, `half-cycles) of the control potential. Under these conditions, an electron which enters the modulating space at a time When the control electrode 351is at a positive maximum will be accelerated. as it traverses the approach space between the Wall portion 3l and` the entrance of the tubular electrode 35. Furthermore, since, it will leave the electrode onehalf cycle later (that is, when the electrode potential isv at a minimum) a second acceleration will occur in the approach. space'between the rightv hand extremity of the electrode 35 and the Wall portion 35.. On the other hand, an electron which enters the modulating vspace in such time phase as to beretarded as it approaches/the electrode 35 will also be retarded as it leaves the electrode. As a result of these successive accelerating and retarding effects, thebeam issuing from the modulating space will be velocity modulated in the/sense that recurrent variations in electron velocity Will exist from point to point along the beam.

The velocity modulation thus produced may be relatively slight if only Weak control potentials are available. Its useful application lies in the fact that a relatively slight amount of velocity modulation may be converted into charge density modulation. of` a higher order of; magnitude by means novv to be described.' The principle involved in the conversion may best be understood by reference to the explanatory representations shown in Figsl 2 and 3 (see second sheet of drawings).

In the rst `of these iigures 'there is shown an electron beam as it is assumed to issue from the modulating space. It Will be seen that this beam comprises ari-.alternate arrangement of fast and slow electrons, the former being represented by black dots a and the latter by light dots b. In Fig. 3, the same beam is shown at a somewhat laterperiod. At this time the fast electrons have, by virtue of their greater velocity, overtaken the slower electrons and become grouped with them. Accordingly, the electron beam as a Whole has become charge density modulated in the sense'that recurrent variations in charge density occur from point to point along its axis.

Thechangevvhich has taken place is from its nature one that requires only the lapse of time and-the absence of extraneous influences which might tend adversely to afect conditions Within the beam. These requirements may be fulfilled in a'practical manner by permitting the velocity modulated beam to pass through a relatively long drift space which yis free from any but static potentials. In the arrangement which is shown in Fig. 1 the drift space may be considered to comprise roughly that portion of' the envelope Whichy is co-terminous with the intermediate tubular conductor 33. This tube serves to shield the drift space from external elds.

From the discussion given above it might seem that with an appropriate length of driftspace even the slightest amountk of velocity modulation could be converted into 100% charge density modulation or, in other Words, thatl the maximum*y obtainable charge density modulation is independent of the velocity modulation. That this is not the case is due primarily to the action of space chargeY (that is, ofthe mutualv repulsion of electrons) in opposing the electron grouping which is characteristic Vof a charge density modulated beam; What ractually takes place may best be understood by comparing the electron beamv to an elongated tube oiA a highly elastic solid material such as rubber,

In this connection, let it be assumed that such a tube is being moved longitudinally through space so as to simulate an electron beam vhaving constant average velocity.- If a momentary retarding'force be Vappliedto-'one"end ofthe tube and-a momentary'accelerating 'force Vto the other end, a Vprocess of compression isfinitiated; Although the average velocity oi `the tube as a whole may not be aiected, the forces-'in question start a relative motion of certain elements oi the tube from its ends towards'its center.` After a certain time this motion will cease as a result of compression of the intermediate region of the vtube.

After the-maximuml compression is reached, the elasticity of the medium produces a restorative motion of the displaced elements toward the ends of the tube. I-Iere again compression-and cessation of suchV motion occurs' and the whole process will be repeated. If the medium in question is perfectly elastic, an indefinite number 'of repetitions are possible, periods of maximum compression being alternated with periods of maximum mobility. It will be understood that during all these periods the tube as a whole is continuing its motion through space.

This is considered to be the sort of thing which happens in an electron beam which has been subjected to velocity modulation. With the passage of time (that is, with the passage ofthe velocity modulated beam through space), the action of the faster electrons in overtaking the slower ones produces compressions or localized increases in electron density. As soon as maximum charge density is attained, i. e., as soon as the mutually repulsive forces of the electrons become sufficient to prevent their further compression, electron dispersion is initiated. This, in turn, over-shoots, so to speak, thus producing further compressions, and so on. The variations of compression may be referred to as the charge density modulation of the beam, while the variations of velocity comprise its velocity modulation.

Taking into consideration the space charge factor, it may be shown that the distance (drift space) required to be traversed by the beam for conversion of the initial velocity modulation into the maximum possible charge density modulation is independent of vthe magnitude `of the velocity modulation for small amounts of the latter. It is, however, a function of the beam velocity, the average charge density of the beam,A the modulating frequency, the diameter of the beam, the diameter of metal and glass parts surrounding the beam and of the magnitude of any external electrostatic or magnetic forces acting on the beam. An approximate formula which has proven useful in determining the proper length of the drift space is as follows:

where LM represents the maximum length of the driftA the dimensions of the envelope and electrode parts. For most practical cases it will fall between 1.0 and 2.0 and may be assigned a average value of 1.3. n

Once the physical. length of the drift space has been fixed by utilization of this formula, a'

final optimum adjustment` may be obtained by varying the beam velocity from the value used in the computation. The best adjustment may be determined objectively by vcontinuously varying the potential applied between the cathode vention such means may -comprise a' feedback' beam. This result is obtained most satisfactorily when the length of the tubular electrode 4l corresponds approximately to the spacing between adjacent charge density maxima and minima in vthe beam. Under these conditions, the approach of a charge density maximum will coincide with the recession of a charge density minimum and a resultant current pulse will be induced inthe electrode. Another current pulse, of opposite sign, is induced a half-cycle later when the approach of a charge density minimum coincides with the recession of a charge density maximum.

In order that these current variations may produce corresponding variations in the potential of the control electrode 35 a Suitable connection must be provided between that electrode and the electrode 4I. For oscillator operation this connection preferably comprises a circuit which is resonant at the desired frequency of oscillation. If this condition be fulfilled the system may be maintained in self -sustained oscillation by mutual reaction with the beam.

For ultra high-frequency operation, it is diiicult to form a satisfactory circuit from conventional circuit elements. It is, therefore, preferable to utilize as a feed-back connection conductive elements which inherently function as a resonant transmission line. In the arrangement shown in Fig. 1 these elements comprise an outer tubular conductor 44 and an inner concentric conductor 4I, the two in combination forming a co-axial transmission line which is open-circuited at both ends. Because of thefresonance in this line the structure may be referred to as a space-resonant device. For resonant operation, the theoretical optimum length of such a. line is a half-wave length or a number of halfwave lengths. However, because of the capacitive end loading caused by the electrodes, the line itself, insofar as it consists of the combination of the conductors 44 and 45 should be somewhat less than the theoretical length.

If it be assumed that the system described is started in oscillation, say by virtue of random electron velocity variations in the beam, sustained operation will ensue. In this operation, velocity modulation is produced by potential variations of the electrode 35; the velocity modulation is converted into charge density modulation in the drift space within the tube 38, and the reaction of the charge density modulated beam on the electrode 4l and the transmission line maintains the system in a state of continuous oscillation.

In order that energy may be taken from the oscillating system thus established and fed to an external utilization circuit, some additional means of coupling to the beam must be provided. In Fig. 1, this is accomplished by coupling capacitivelyto the electrode 4l by means of a conducting plate 41 positioned in proximity thereto. This plate may constitute one terminus of a conductor 48 which forms the inner member of a concentric "transmission line the inner and outer conductors of which lcomprise a space-resonant end loading requires a compensatory foreshortening of the line and results in inconveniently small parts.) This may be done with diminishing the number of approach spaces by the use of a construction such as is shown in Figs 8 and 9. In this embodiment the transmission line comprises the combination of an outer conductive shell 95 and an inner tubular structure which is within the shell and extends longitudinally thereof. These parts in combination form a line which is closed at its ends by means of transverse wall members 98 and 99 extending between the extremities of the shell and the tubular structure.

The tubular structure referred to comprises a series of conducting tubes numbered |00, and |02 respectively, the tubes being relatively spaced so as to provide gaps between them. These gaps are conductively bridged by means of metallic elements |03 connecting with the various tubes. In each of the gaps there is provided a tubular electrode (indicated at |05 and, |06) which corresponds in nature and function to the electrodes 35 and 44 described in connection with Fig. l. In this case however, the electrodes are directly electrically connected to the shell 95 by means of metallic members |08 extending between them (see Fig. 9). Consequently, assuming that the shell 95 is solidly grounded, it may be considered that the electrodes |05 and |06 are maintained at a fixed invariable potential. On the other hand potential variations (resulting from the creation of a standing wave) may be caused to occur from point to point along the elements |00 to |03. As a result of the oscillatory variations of the standing wave, the extremities of the tubes |00, |0| and |02 nearest to the electrodes |05 and |06 will be caused to rise and fall in potential with respect to these electrodes. Consequently, velocity variations of the beam will be produced adjacent to former electrode while feed-back will occur at the latter as a result of charge density variations in the portion of the beam which traverses it.

The combination just described may alternatively be operated as a full wave or a half-wave transmission line. In either case satisfactory operation will result if the beam velocity be properly correlated to the length of the tubular 'elements |0|, |05 and |06. As to the element |0| the correlation should be with a view to obtaining substantial charge density modulation in the drift space provided within that element. As to the electrode |06 on the other hand, the best operating condition is that in which the length of the electrode corresponds, at least approximately, to the spacing between adjacent charge density maxima and minima in the beam.

It will be noted that with the construction of Fig. 8 the area of the electrodes |05 and |06 which is exposed to parts at a different potential,

from the electrodes is relatively small. (This is a result of the fact that most of the parts which surround the electrodes are directly electrically connected to them.) Consequently the capacitive loading imposed on the feed-back system by f the presence of these electrodes is appreciably less than in the constructions of Figs. l to 6. It is. therefore, possible to make the transmission line function as a half-wave line without such compensatory shortening of its parts as would make their dimensions impracticably small.

While I havedescribed my invention in connection lwith particular structures, it will be un derstood that many modifications may be made by those skilled in the art without departure from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as fall within the true spirit and. scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In high frequency apparatus, the combination which comprises means for producing a beam of electrons, a plurality of valined tubular conductive members mutually spaced to permit the establishment of potential gradients acting on the beam at a plurality of points along its axis, the said members being dimensionally cor,- related to the velocity of the beam so as to assure eiective mutual reaction with the beam for a desired condition of operation of the apparatus, and a conductive shell coaxially surrounding the said members, the said shell serving by virtue of its electrical coaction with the members to provide effective feed-back between members last traversed by the beam and those initially traversed by it, thereby to maintain the apparatus in self-sustained oscillation at a frequency corresponding to the said desired condition of operation.

2. An oscillator comprising means for developing an electron beam, means including a control electrode structure effective to produce velocity modulation of the beam without producing appreciablecharge density variations in the vicinity of the electrode structure, means providing a drift space to be traversed by the beam after production of such velocity modulation, the drift space being4 sufilciently vlong to effect transformation of the Velocity modulation into charge density modulation, and means functioning as a transmission line resonant at the desired frequency of oscillation of the oscillator for providing feedback coupling between the control electrode structure and the portion of the beam issuing from the drift space. *y

3. An oscillator comprising an elongated tubular envelope, means for projecting an electron beam longitudinally through the envelope, a first vset of conductive elements coupled to the beam tion, the drift space being sufficiently long to effect transformation of the velocity modulation into charge density modulation of a higher order of magnitude, means providing a feed-back coupling between the portion of the beam issuing from the drift space and the said conductive elements thereby to maintain the oscillator in selfsustained oscillation, and another set of conductive elements coupled to the last-mentioned portion of the beam independently of the feed-back means for abstracting energy from the beam.

4. The combination which includes means for producing an electron beam, means for velocity modulating the beam, means providing a drift space of substantial length to be traversed by the beam after velocity modulation thereof, ccnductive elements coupled to the portion of the beam issuing from the, drift space, a conductive shell surrounding the beam and extending longitudinally thereof at least throughout the region which comprises the drift space, and means within the shell forming therewith a resonant trans mission line connecting between the said conduc- 111 tive elements and the velocity modulating means. thereby to maintain the l system in self-sustained oscillation.

5. Thecombination which includes meansior producing an electronjbeam, conductive elements for producing potentialgradients acting longitudinally on the beam at two spaced regions thereo, the VVsaid regions being sufficiently spaced so that electron velocity variations produced vby gradients acting .at the'region nearer .the .beam source may beconverted into appreciable charge density variations the distance intervening between the regions,xand an elongated conductive vshell surrounding the beam pathand the conductive elements and forming in conjunction with the said elements fa resonant transmission line adapted to function 4as .afeed-back connection between the two regions, thereby to mainv tain the combination in Seli-sustained oscillation.

6. The combination, which includes means for producing anelectron beam,` a pair of concentric tubular metal shells surroundingthe beam path for asubstantialportion of its length, the inner shell being appreciably shorter than the outer shell and being directly electrically. connected thereto, -means projecting inwardly from the ends of the outer shell so as to provide conductive surfaces .in spaced opposed relationship to the extremities of theinner shell,r a pair of tubular electrode elements respectively positioned in the spaces between the said surfaces and the said extremities and cooperatingtherewith to permit the establishment of potential gradients acting on the beam, and means connecting the said electrodes and forming in conjunction vwith the tubular shells a resonantcircuit adapted to be maintained in oscillation by `mutual reaction with the beam.

'7. The combination vwhich includes meansfor producing an electron beam, a tubular member surrounding the beam path'for an appreciable portion of its length, aconductive shell concentric with and surrounding the said tubular mem.- bermeans conductively connected .with the said shell and cooperating with the extremities of the tubular member to permit the .production of po'- tential gradients acting longitudinally on the beam adjacent such extremities, lthe tubular member and theshell comprising' in combination a resonant circuit which is maintained in oscillation bv the reaction of thebeam, andmeans coupled` to the prnrtionzcf` the beam 'issuing from the tubular memberl forf receiving energy z therefrom.

8. An oscillator includingzan anode and cathode for producing an electron beam, an elongated conductive shell enclosing thepathof the beam, a conductive tubularstructure within the shell and forming therewith a resonant transmission line. said tubular structure also enclosing the path of the electron. beam and being provided with a pair of spaced-gaps, conductive means bridging said gap-5,. and electrode members in said gaps connected to the yconductive shell so as to be maintained at a fixed potential with respect thereto, the electrode members and the tubular structure cooperating through the intermediation of the electron beam to maintain the transmission line in self-sustained oscillation,

and means coupled with the beam after its passage through the conductive shell for receiving energy from the beam.

A.9., An. electron discharge device' having a tank l circuit including a pair of concentric tubular conducting members whicnin combination; form astanding .wave'system, a further conducting member spaced axially from the inner tubular member to provide a gap therebetween, said 5 vfurther member4 being permeable to electrons and being electrically connected to the outer tubular member, meansfor projecting a stream of electrons ,axially of said tubular members and across ksaid gap,..and means for modulating 'said stream prior to its passagey across the gap, thereby to produceexcitation of the tankcircuit.

10. An electron discharge device having a tank circuit including a `pair of concentric tubular members'which, in combination, form -a standing wave system, vanother,tubular member' coaxial with the inner of'the two concentric tubular vmembers and axially spaced therefrom to provide a gap between the members, said other member being electrically'connected to the outer concentric member, means for projecting a stream of electrons axially V of said tubular members across said gap, means -ior modulating said stream of electrons prior to vits passageacross said gap and'means for collecting the electrons after passage through said 'tubular members.

1l. An electron discharge device having a tank 'circuit including a pair of concentric tubular conducting members which, vin combination, form astanding wavesystem, a `,further conducting member spaced axially from lthe-'inner tubular member to vprovide a gap therebetween, said further member vbeing permeable to `electrons and being electrically connected to lthe' outer tubular memben'means'for Vprojecting a stream of electrons axially of said tubular members Iand across said gap, and means adjacentthe end of the inner tubular lmember more remote from the `gap for modulating/the electron stream at airequency corresponding to theresonant frequency 40 of the tank circuit, thereby' to produce excitaltion' of such circuit by'pa'ssage of the v.modulated electron" stream vacross the gap.

12. An electron :discharge device including a tank-*circuit having. a pair 'oi coaxial 'tubular mem- 45 bers lspaced axially to forma gap anda concentricf'outer tubular member forming 4a'standving-wave systemfiwith lone of said coaxial-tubular members, a cathode yand grid positioned adjacent one end of one yoi said' pair vof coaxial tubular f5() .members for `projecting an electron `stream axially -of said coaxial 'tubular members and facrosszsaid `gap to lexcite the said standingtwave system,` and 7a'collecting electrode for receiving the' electron stream after vTits .traversal of ithe'said tubular v55 tmembers.

' 13.' Electric discharge .apparatus including'. an elongated hollowelectrode'which is Venabled to resonate asa standing wave system by'virtue of its relationship to the other Vparts of the B0 apparatus structure, apair'of electron permeable conducting members which form lparts of the apparatus structure Aand ywhich yare 'respectively `spaced from `the extremitiesoi the said electrode to provide gaps'a'djacent such extremities, and

V l`55 means for projecting an electron'stream through the said conductive members and'axia'lly of the electrode, thereby to produceexcitation .of Vthe lsaid standing Wave system by the action ofl the 'stream at the said gaps.

14. Electric discharge lapparatus including an elongated hollow electrode7 conductive ymeans yconstitutinga part of the saidapparatus structure and positioned in'proximity to the said electrode, the electrode forming in conjunction with the said conductive meanslaresonant standelectron stream through the said conductive,

members and axially of the electrode at such velocity as to produce excitation of the said standing wave system by the action of the stream at the said gaps.

15. IThe combination which includes means for producing an electron beam, a tubular conductive member surrounding the beam pathfor an appreciable portion of its length, a conductive shell surrounding the said tubular member, and further electron permeable conductive members which are respectively spaced from the extremities of the said tubular member to provide gaps adjacent said extremities, the said member and the said conductive shell comprising in combination a standing wave system which is adapted to be maintained in oscillation by the reaction of the electron beam on the members at the said gaps.

16. The combination which includes means for producing an electron beam, a tubular conductive member surrounding the beam path for an appreciable portion of its length. a conductive structure surrounding the said tubular member, means conductively connected with the said structure and cooperating with the extremities of the tubular member to produce potential vgradients acting longitudinally on the beam adjacent such extremities, the tubular-member and the said conductive structure comprising in combination a standing wave system which is adapted to be maintained in oscillation by the reaction ofthe electron beam thereon.

17. Apparatus of the character described having, in combination, means for creating a confined standing electromagnetic eld having an electric eld portion extending in a predetermined region, means for conning `the electric field portion to the region, and means for passing an electron stream through the electric iield portion to cause the electrons -to assume periodically varying velocities and thereafter past the field to cause the electrons to become concentrated in groups.

18. Apparatus of the character described having, in combination, means for creating an electron stream of substantially uniform velocity, a space-resonant device. means for creating a standing electromagnetic field within the spaceresonant device, the exterior surface of said device being free of alternating potentials of the frequency of operation of the apparatus, and means for directing the electron stream through the iield of the space-resonant device to cause the electrons to assume periodically varying velocities due to the action of the internal field therein.

19. Apparatus of the character described having, in combination, means comprising aspaceresonant device for creating an electron stream having the electrons thereof concentrated in.

groups, and means for passing said groups when formed into said space-resonant device for ab- 921. Apparatus of the character described having, in combination, means for creating an elec--v tron stream, means comprising a space-resonant device for periodically varying the velocity of the electrons of the stream, means for causing the electrons of the stream thereafter to become concentrated in groups, and means for passing said group into the eld of said space-resonant device whereby said field absorbs energy from the groups. l

v 22. Apparatus of the character described having,'in combination, means for creating an elec` tron stream, means comprising a space-resonant device for causing the electrons of the stream' to become concentrated in groups, and means comprising said space-resonant device for ab# sorbing energy from the groups. I

23. Apparatus of the character described having, in combination, a space-resonant device, means for producing a grouped electron stream for traversing the space-resonant device, and means comprising the grouped stream for creating an' alternating electromagnetic field in the space-resonant device to absorb energy from the stream, said rst means including means to sub-- ject electrons to said eld to produce said grouped electrons stream.

24. In combination, an apertured hollow mem-f ber having a conducting portion, a second aper-y tured smaller hollow member also having a con; ducting portion suspended within said first memi ber and spaced therefrom to provide a hollow cavity resonator between the outer surface'of said inner member and the inner surface of said outerfmember, means for providing an oscillating electromagnetic field within said hollow cavity 'resonator at a resonant frequency thereof comprising, means for producing a beam of electrons, means for projecting said beam through an aperture of said first member, through the spacejbetween the inner wall of saidv first member and said second member, through said secondvmember and outwardly thereof through a second space between said second memberand said iirst member, to thereby set up 'standing electromagnetic waves between said inner and outer hollow members at the natural frequency of said hollow cavity resonator for cyclically varying the number of electrons emerging from within said inner hollow member into the second space between said inner and outer members, to enhance and maintain the standing waves at the natural frequency oi. said hollow cavity resonator.

25. In a generator of electromagnetic waves comprising an electromagnetically resonant hollow conducting member arranged to have an electric field therein, means for producing a stream of electrons. means for proecting said stream oi. electrons through a portion of the electric field of said resonator wherein energy change is suffered by the electrons of said stream to initiate velocity grouping of electrons, means for shielding said electrons from the eld of said resonator for a time interval sufficient to allow velocity grouping to be completed, and means for projecting said velocity grouped electrons through another portion of the electric eld of said resonator wherein the electrons suifer changes of energy to deliver electromagnetic energy to said resonator.

26. An electron discharge device circuit having a, tank, said tank being comprised of an outer conductor and a single hollow inner coaxlally arranged conductor separated axially at both ends from said outer conductor by gaps, the

length vof said inner conductor betweensad gaps being a multiple including unity of one-half the length of the operating wave corresponding to the resonant period of said tank, a source of electrons for projecting a stream of electrons through the entire length of said hollow inner conductor and across said gaps in succession, and means for attracting and collecting the electrons crossing the last gap to be traversed by said electrons.

27. 1n an electronic apparatus having means for producing an electron beam, a resonant electrode System including a conductive structure surrounding the beam for a substantial portion of its `path length, and including va single r.con-- ductive tubular element a multiple, including unity, of a half Wave .long concentrically positioned within said structure so as to be axially traversed by the beam and spaced at its extremities from said conductive structure to provide a pair of gaps to be traversed by said electron beam, the length of said tubular element being correlated to the average velocity of the beam and to the desired frequency of operation of the apparatus.

28, An electronic device including an electronic gun, means for beaming the electronsfromsaid gun, a hollow resonant electrode for shielding electrons projected from external fields, said resonant electrode having an .effective length equal to an integral number of half wave lengths of the oscillatory currents established thereon, means .for .directing said beam .of electrons through said hollow electrode along its longitudinal axis, and means for adjusting the velocity of the electrons passing through said hollow electrode so that the distribution .of oscillatory potentials along the length .of said electrode. alters the energy of said electrons.

29. An electronic device including a source of electrons, means for beaming said electrons, a hollow resonant electrode for shielding electrons within said hollow from external elds, said electrode having such length thatit resonates at the operating frequency, means for directing said -16 beam through said hollow electrode along its longitudinal axis, and means for adjusting the period of dwell of electrons within said hollow electrode so that the oscillatory potentials on the ends of said hollow electrode alter the energy of electrons entering and leaving said hollow electrode.

30. An electronic oscillator including a hollow resonant electrode for shielding electrons within said hollow from external elds, said electrode having .such a length that it resonates at the operating frequency, means for establishing a beam of electrons, means for directing said beam through said electrode along its longitudinal axis, and means for adjusting the velocity of said electrons lwithin said electrode so that oscillatory currents are created and sustained in said electrode as a function ef its resonant characteristics.

v31. In a device of the character of claim 28, an apertured diaphragm electrode adjacent the hollow end of said resonant electrode, and means for adjusting the electron transit time between said `last two electrodes.

32. In a device of the character of claim 28, apair of apertured diaphragm electrodes located at the opposite ends of said resonant electrode, and means for adjusting the electron transit times between said diaphragm electrodes and said hollow electrode ends.

WILLIAM C. HAHN.

REFERENCES CITED The ollowingreferences are of record in the file of this. patent:

` UNiTED STATES PATENTS Number Name Date 2,096,460 Llewellyn Oct. 19, 1937 A2,147,454 Morton Feb. 14, 1939 2,190,511 Cage Feb. 13, 1940 2,190,668 Llewellyn Feb. 20, 1940 FOREIGN PATENTS Number Country Date 431,447 Great Britain July 8, 1935 Certificate of Correction Patent No. 2,498,886 February 28, 1950 WILLIAM C. HAHN It is hereby certified that error appears in the printed specication of the above numbered patent requiring correction as follows: I

Column 9, line 3, for the Word With" read without;

and that the said Letters Patent should be read with this correction therein that. the i same may conform to the record of the case in the Patent Oce.

Signed and sealed this 25th day of July, A. D. 1950.

[SML] THOMAS F. MURPHY,

Assistant Uofmnz'ssz'oner of Patents. 

